A comparative thermodynamic characterization of the large fragment domains of Taq (Klentaq) and E. coli (Klenow) DNA polymerases reveals that Klentaq's extreme free energy of folding originates from a decreased entropic folding penalty.  Parallel solution-based structural analyses reveals that the denatured state of the mesophilic polymerase (Klenow) is more elongated than the denatured state of the thermophilic Taq polymerase and thus has a significantly larger radius of gyration.  The combined data indicate that the folded state of the thermophilic polymerase is not more intrinsically stable:  instead, its more globular denatured state has a considerably reduced entropic and structural barrier between the denatured and native states, resulting in a much more favorable ?G of folding.  This is the first direct structural demonstration of denatured state size/shape differences in a mesophilic-thermophilic protein pair.  Despite their demonstrably different sizes and structures, both denatured state ensembles still fall within the range of random-coil behavior.

Why is Taq DNA polymerase so stable?   A reduced entropic folding penalty and the shape of the denatured state ensemble

245th National Meeting (2013)

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